Dispatching event from any component by either by using this or simply without thiscan not be listen by each and every componet of the application,depends upon where you have write addListner. Check Event life cyclein the flex. While if you are using the system manager for dispatching the event and also for listenting the event so in that case you will always listen the event.

You can visit this link for making it simple to use and understand.By this way you can always listen your event inside any component in your application.